1. Field of the Invention
The present invention relates to a method of measuring the temperature of a workpiece (object of measurement), such as a semiconductor wafer, and relates to a temperature control method and a processing apparatus.
2. Description of the Related Art
Generally, when fabricating a semiconductor integrated circuit, a semiconductor wafer, such as a silicon wafer, needs to be repeatedly subjected to various processes including film forming processes, annealing processes, oxidation-enhanced diffusion processes, sputtering processes, etching processes and the like. To carry out these processes accurately, the temperature of the semiconductor wafer must be strictly controlled to maintain the semiconductor wafer stably at a desired process temperature.
A general single-wafer processing apparatus has a susceptor having the shape of a disk or a circular cylinder, and a temperature sensor, such as a thermocouple, embedded in the support surface of the susceptor. A temperature of a wafer, placed on the susceptor, is indirectly measured by the temperature sensor. A heater is controlled in a feedback control mode on the basis of measured temperature of the wafer to maintain the wafer at a desired temperature.
It is difficult to measure the actual temperature of the wafer accurately by the above method employing the thermocouple because the temperature of the wafer is lower than that of the susceptor by 10 to 40xc2x0 C. depending on process pressure.
The temperature of the wafer in process may be measured by bringing a thermocouple into contact with the wafer while the wafer is being processed. However, it is difficult to bring a thermocouple into contact with a wafer being processed. It is scarcely possible to measure the temperature of a wafer by bringing a thermocouple into direct contact with the wafer while the wafer is being processed particularly when the wafer is processed by a processing apparatus in which the wafer is rotated during the process.
Therefore, a radiation thermometer capable of measuring temperatures relatively accurately in a non-contact mode has been used in recent years. The radiation thermometer measures the radiance of a semiconductor wafer, i.e., an object of measurement, to determine the temperature of the wafer from the measured emissivity.
It is known that the emissivity of a semiconductor wafer is considerably dependent on the condition of the surfaces, i.e., the upper and lower surface, of the wafer when the water is subjected to a heat treatment. Therefore, the emissivity of a wafer is dependent on the type of a film formed on the surface of the wafer. Generally, a plurality of types of films are deposited in multiple layers on the surface of a wafer, and a processing apparatus is required to process wafers respectively having different surface conditions. Therefore, when the temperature of the wafer being processed is measured, predetermined thermal emissivities corresponding to the temperature thereof for films of different types are fixedly used and a measured radiance is corrected by calculation.
Generally, the interior of a processing vessel in which the radiation thermometer is installed is an environment in which multiple reflection occurs (hereinafter referred to as xe2x80x9cmultiple reflection environmentxe2x80x9d). Therefore, light reflected several times falls on the radiation thermometer in addition to light that falls directly on the radiation thermometer and, consequently, it is difficult to measure the actual temperature of a wafer in such an environment with a sufficiently high accuracy.
Although the performance of the sensing device of the radiation thermometer is scarcely subject to change with time, the performance of lenses included in an optical system that guides light emitted by a workpiece placed in a processing chamber to the radiation thermometer is subject to change with time due to, for example, dimming, which introduces errors in measured temperatures. A method capable of solving such a problem is disclosed in JP-A No. Hei 11-51769. In this prior art method, light emitted by a light source is reflected by a semitransparent mirror toward a lens to project the light through the lens on an object of measurement. Reflected light reflected by the object travels through the lens and the semitransparent mirror to a sensing device. The intensity of the light emitted by the light source and that of the reflected light measured by the sensing device are compared to estimate the degree of change of the performance of the lens with time. When actually measuring the temperature of an object, the intensity of the reflected light measured by the sensing device is corrected according to the change of the performance of the lens to calculate the temperature of the object. This method, however, needs a temperature measuring system provided with a complicated optical system including a semitransparent mirror.
Accordingly, it is an object of the present invention to provide a temperature measuring method capable of measuring the temperature of an object of measurement (workpiece) with a high accuracy in a multiple reflection environment, and a temperature control method using this temperature measuring method.
A second object of the present invention is to provide a measuring error correcting means of simple construction for correcting measuring errors attributable to a change in the performance of an optical system with time.
A third object of the present invention is to provide a thermal processing apparatus using the temperature measuring method and the measuring error correcting means and capable of high repeatability of process.
The present invention provides a temperature measuring method for measuring a temperature of an object of measurement placed in a multiple reflection environment by using a radiation thermometer. In this method, effective emissivity xcex5eff is used for calculating the temperature of the object. The effective emissivity xcex5eff is defined by an expression:
xe2x80x83xcex5eff=(1xe2x88x92xcex1)xc2x7xcex5+xcex1xc2x7xcex5/{1xe2x88x92Fxc2x7rxc2x7(1xe2x88x92xcex5)}
where F is view factor, xcex5 is the emissivity of the object, r is the reflectivity of a reflecting plate included in the radiation thermometer and xcex1 is a weighting factor for compensating effects of multiple reflection.
The present invention also provides a temperature control method and a processing apparatus that use the above method.
The temperature measuring method takes the effect of multiple reflection into consideration by using the weighting factor to measure the true temperature of the object accurately. A heating means included in a processing system is controlled on the basis of the temperature of the object measured on the basis of the foregoing principle of measurement to carry out processes of a high quality in excellent repeatability.
The present invention also provides a processing apparatus, which includes; a processing vessel in which a workpiece is placed; a heating means for heating the workpiece; a light-emitting device that emits light; a radiation thermometer that outputs an signal representing a numerical value corresponding to an radiance of the workpiece; an optical system for guiding light from the light-emitting device to the workpiece and from the workpiece to the radiation thermometer, the optical system including: a first optical fiber having a first end optically connected to the light-emitting device to guide light emitted by the light-emitting device to the workpiece; a second optical fiber having a first end optically connected to the radiation thermometer to guide light from the workpiece to the radiation thermometer; and a lens optically connected to a second end of the first and the second optical fiber; a processor calculating a numerical value representing a condition of the optical system on the basis of an intensity of light emitted by the light-emitting device, guided to the workpiece by the first optical fiber and the lens, reflected by the workpiece and guided by the lens and the second optical fiber to the radiation thermometer, the processor calculating a temperature of the workpiece based on the numerical value corresponding to an radiance of the workpiece and a numerical value representing a condition of the optical system; and a controller that controls the heating means on the basis of the temperature of the object provided by the processor.